Preston, a former Army medic, says he was asked to train Jeffrey Dahmer in July 1979 while they were both stationed in Germany. Preston says they were on a field exercise in Belgium when, he claims, he was drugged and raped by Dahmer but blocked out the attack. Years later, he says he was looking at a serial killer website when he learned he was referenced in a book called “The Shrine of Jeffrey Dahmer,” by Brian Masters.

“It mentioned me by name,” says Preston in the video above.

Watch more of Preston's story in part one of this three-part Dr. Phil, “In The Presence of Evil: Face to Face with Jeffrey Dahmer,” airing Tuesday. And later, Billy, also a former Army medic, shares his story of being repeatedly drugged, raped, and brutally assaulted by Dahmer.

Plus, Dr. Phil talks to the sister of one of Jeffrey Dahmer’s victims, who says the new Netflix series, Dahmer - Monster: The Jeffrey Dahmer Story, has glorified the man she calls “Satan.”

Then, tune in Wednesday for part two, “Raising Evil: The Interview with Jeffrey Dahmer's Father,” when Dr. Phil reveals his never-before-seen interview with the serial killer’s father and stepmother.

Check your local listing for airtimes.

WATCH: Army Veterans Who Served With Jeffrey Dahmer Say They Believe He Was Killing Even Then

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